Open loop wake-up radio based on transmitter fingerprinting

ABSTRACT

A device (e.g., an IoT device) includes a first radio, and a memory device accessible to the first radio. The memory device is configured to store a fingerprinting feature for a specific transmitter device. A second radio and a processor are also included. The process is coupled to the first and second radios. The first radio is configured to extract a fingerprinting feature of a first received wireless signal, determine that the extracted feature matches the fingerprinting feature stored in the storage device, and responsive to the determination that the extracted feature matches the feature stored in the storage device, cause the second radio to transition from a lower power state to a higher power state of operation and continue to receive the incoming signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/858,119, filed Apr. 24, 2020, which is incorporated by referenceherein in its entirety.

BACKGROUND

One challenge in a wireless network that includes battery-operateddevices is battery life. One type of wireless device is anInternet-of-Things (IoT) device. IoT devices often have a sensor usableto monitor an environmental condition (e.g., temperature), the operatingstate of a machine, or other type of condition. IoT devices generallyare “headless” meaning that they have no direct user input/outputcapability (e.g., no keyboard, no display, etc.). IoT devices are oftenbattery-operated and are installed within an environment or machine andare not intended to be directly accessed by a user. Many applicationsfor the use of IoT devices benefit from the IoT devices' batterieslasting a long time (e.g., years).

SUMMARY

In at least one example, a device includes a first radio, and a memorydevice accessible to the first radio. The memory device is configured tostore a feature for a specific transmitter device. A second radio and aprocessor are also included. The process is coupled to the first andsecond radios. The first radio is configured to extract a feature of afirst received wireless signal, determine that the extracted featurematches the feature stored in the storage device, and responsive to thedetermination that the extracted feature matches the feature stored inthe storage device, cause the second radio to transition from a lowerpower state to a higher power state of operation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 illustrates a wireless network including IoT devices inaccordance with an example.

FIG. 2 shows an example implementation of an IoT having a wake-up radio.

FIG. 3 shows an example of a method for an IoT device to validate anaccess point based on a feature extracted from a wireless signal.

DETAILED DESCRIPTION

Some battery-powered wireless devices include a “main” radio and a“wake-up” radio. The main radio is used to transmit and/or receive datain accordance with the device's runtime operation. The main radio canenter a low power state (e.g., a sleep state, hibernation state, etc.)during periods of non-use. The wake-up radio receives wireless signalsfrom transmitters in the wireless network to determine when to wake-upthe main radio. Wake-up radios may operate in an “open loop”configuration or a “closed loop” configuration. A closed-loop wake-upradio is preconfigured to recognize, for example, a certain sequence ofsymbols from a transmitter, or negotiates with the transmitter for thetransmitter-specific sequence of symbols. Closed-loop wake-up radios andtransmitters may follow a particular wireless protocol that determineand/or negotiate a wake-up signal. The negotiation of the wake-up signalis in addition to the data and message signaling.

Although wireless devices operate according to applicable standardprotocols (e.g., IEEE 802.11, Bluetooth Low Energy, etc.), a wirelesstransmitter within a given wireless network can be distinguished fromother wireless transmitters due to imperfections in the analogcomponents of the transmitter. Such imperfections may result fromrandomness introduced during the manufacturing of the components of thetransmitters (e.g., digital-to-analog converters, filters, frequencymixers, power amplifiers, etc.). For example, the threshold voltage oron-resistance of metal oxide semiconductor field effect transistors(MOSFETs) may vary slightly from transistor to transistor even thoughthe transistors are made in accordance with the same process steps. Suchnon-linear effects result in each transmitter having a unique“fingerprint.” Thus, radio frequency (RF) fingerprinting can be used bya receiver to identify a specific transmitter from among other possibletransmitters to thereby wake-up the main radio. Waking up the main radiobased on an RF fingerprint is an “open-loop” process in that anegotiation of a particular set of symbols between transmitter andreceiver is not required. That is, a wake-up signal (generated internalto the wireless device) to wake a main radio in response to an aspect ofa specific transmitter (an extracted “feature”) is generated based onthe transmitter's standard transmission without adding anyspecific/integrated wake-up signal to the normal data transmissionprotocol. The receiver determines the RF fingerprint of a transmissionthat uniquely identifies a particular transmitter with which thereceiver is to associate, and then uses that extracted feature to onlywake-up the main radio when the valid feature is detected, for example,the extracted feature matches a feature stored in the radio's memory).The transmission being fingerprinted may also include an identifier ofthe IoT device(s) that the transmitter wants to wake. Fingerprinting atransmission with the IoT device-specific identifier will cause onlythat particular IoT device to wake its main radio when a futuretransmission with the relevant fingerprint is detected.

The disclosed examples are directed to a battery-powered,Internet-of-Things (IoT) devices that include a main radio and a wake-upradio. The main radio is used by the IoT device to transmit and/orreceive data in accordance with its runtime operation. In one example,the battery-powered IoT device may have one or more integrated orexternal sensors, and the IoT device's main radio is used to transmitsensor data or event information to the wireless network. To savebattery power, the main radio transitions to a lower power state (e.g.,a sleep or hibernation state). While in the lower power state, the mainradio is not usable to send or receive wireless signals. Instead, themain radio must be woken up for that purpose. The wake-up radio employsRF fingerprinting (i.e., a temporary “feature”) to detect when a validtransmitter (e.g., an access point) is attempting to communicate withthe IoT device containing the wake-up radio. In this context, a validtransmitter is a transmitter to which the IoT device is paired and withwhich the IoT device should communicate. When the wake-up radio detectsa valid fingerprint, the wake-up radio causes the main radio to wake up(i.e., transition from the lower power state to the higher power state)and to continue decoding the received wireless signal to thereby becapable of runtime operations such as transmitting sensor data,receiving wireless communications from the transmitter, etc. The wake-upradio described herein thus employs RF fingerprinting (e.g., comparing anewly extracted feature to one or more features stored in memory) towake up the main radio. Because the wake-up event is generated whilealso receiving data in the course of normal operations (i.e., there isno dedicated wake-up signal), a negotiation of a specific set ofdedicated wake-up symbols between transmitter and receiver according toa specific protocol is not needed for the open-loop wake-up radiodescribed herein.

FIG. 1 shows an example of a wireless network 100 including accesspoints 110 and 111 and IoT devices 120 and 130. Any number of IoTdevices (one or more) can be included within the wireless network 100.In this example, each IoT device includes a battery, a main radio and afingerprinting wake-up radio (WUR). IoT device 120 includes a battery121, a main radio 122, and a fingerprinting wake-up radio 126.Similarly, IoT device 130 includes a battery 131, a main radio 132, anda fingerprinting wake-up radio 136. During extended periods of non-use,the main radios 122, 132 of the IoT devices 120, 130 are turned off tosave battery power. However, the fingerprinting wake-up radios 122, 132remain continuously powered on. In the configuration of FIG. 1 , mainradio 132 in IoT device 130 is turned off. The wake-up radio 126 in IoTdevice 120 has detected a valid fingerprint from a wireless signaltransmitted by access point 110 (e.g., has extracted a feature from thewireless signal and determined that the feature matches a feature storedin the radio's memory). In response to detection of a valid fingerprint,the wake-up radio 126 causes the main radio 122 in IoT device 120 towake to complete the reception on the arriving wireless signal (e.g.,powered on or otherwise transitioned to a higher power, fullyoperational state). The wake-up radio 136 in IoT device 130 is notconfigured to recognize the same RF fingerprint as wake-up radio 126(e.g., the feature extracted by wake-up radio 136 does not match anyfeatures stored in that radio's memory), and thus the main radio 132 inIoT device 130 remains in a low power state (e.g., sleep, hibernation,etc.). Instead, the wake-up radio 136 of IoT device 130 may beconfigured to recognize an RF fingerprint derived from access point 111.

FIG. 2 shows additional detail regarding the implementation of IoTdevice 120, but the same architecture may apply to IoT device 130 and/orother IoT devices in the wireless network 100. In this example, IoTdevice 120 includes battery 121, main radio 122, fingerprinting wake-upradio 126, a processor 210, a sensor 220, and a memory device 227. Themain and fingerprinting wake-up radios 122 and 126 as well as sensor 220are coupled to processor 210. The battery 121 provides operating powerfor some or all of the active components with in the IoT device 120.While one processor 210 is shown in this example, more than oneprocessor can be provided in other implementations. Similarly, more thanone sensor 220 can be provided as well. The sensor 220 isapplication-specific. Examples of sensor 220 include a temperaturesensor, a current sensor, a voltage sensor, etc.

Each radio 122, 126 is coupled to an antenna. Main radio 122 is coupledto antenna 225, and wake-up radio 126 is coupled to antenna 235. Eachradio thus may be connected to its own antenna. In other example, oneantenna or antenna array is shared between the two radios 122, 126. Asnoted above, the main radio 122 is used for a different purpose than thefingerprinting wake-up radio. The main radio 122 is used to exchange(send and/or receive) wireless signals with an access point duringdevice run-time. For example, the main radio 122 may be used to receivea request from an access point (e.g., access point 110) for a sensorreading, send data and/or signals from sensor 220 to the access point(e.g., access point 110), etc. In an implementation in which IoT device120 responds to requests received from an access point, the main radio122 in the IoT device may be powered off followingtransmission/reception of information to the access point as the IoTdevice awaits another request from the access point. Alternatively, themain radio 122 may be powered down following a predefined period of timeof non-use (e.g., 30 second, 2 minutes, etc.).

The fingerprinting wake-up radio 126 remains continuously powered on andoperational in at least some implementations and is used to detect avalid fingerprint from an access point's standard wireless signals. Inresponse to detection of a valid RF fingerprint, the main radio 122 iscaused to be transitioned from the lower power state to the higher powerstate in order to receive the incoming signal.

RF fingerprinting can be performed based on the following illustrativecategories: transient-based RF fingerprinting and steady-state based RFfingerprinting generation. In transient-based RF fingerprintinggeneration, a transmitter transmitting from its off to on statestriggers a unique transient feature within the transmitted wirelesssignal which appears before the transmission of the actual packet ofdata. In steady-state based RF fingerprinting generation, uniquefeatures are present in the transmitter's wireless signal during themodulation phase. In this case, the fingerprinting wake-up radiogenerates the fingerprint from at least one received symbol. Any ofnumerous different types of RF fingerprinting techniques can beimplemented by an IoT device to validate a transmitter. Validating thetransmitter means that the IoT device confirms whether a wireless signalthe IoT device receives is from a transmitter with which the IoT deviceis associated (e.g., paired) and the extracted feature matches a featurealready stored in the device's memory).

One example of transient-based RF fingerprinting includes thedetermination of the power spectral density (PSD) of the preamble in,for example, an IEEE 802.11a preamble. In this particular RFfingerprinting technique, the PSD is characterized by PSD coefficients,which can be calculated as:

${PS{D_{X}(k)}} = \frac{\left| {X(k)} \right|^{2}}{\left. \Sigma_{k = 1}^{K} \middle| {X(k)} \right|^{2}}$where X(k) are the coefficients of a discrete Fourier transform of theinput signal x(m) and are given by:

${X(k)} = {\frac{1}{N_{F}}{\sum_{m = 1}^{N_{F}}{{x(m)}e^{\lbrack{\frac{{- 2}\pi j}{N_{F}}{({m - 1})}{({k - 1})}}\rbrack}}}}$

The PSD of a wireless signal received from a transmitter can be used touniquely identify the transmitter. That is, the PSD varies betweentransmitters and is generally repeatable for a given transmitter. Thefingerprinting wake-up radio described herein is usable to determine thePSD for an incoming wireless signal. The PSD for one or moretransmitters to which an IoT device is associated is stored in memory227 within the IoT device as fingerprint(s) 229. The PSD determined fora given wireless signal can be compared to the PSD(s) stored in memorywithin the IoT device to determine whether a valid transmitter isattempting to communicate with the IoT device. If the PSD computed bythe IoT device matches a PSD stored in the IoT device's memory, then themain radio is caused to be transitioned from its lower power state toits higher power state (i.e., awakened).

The fingerprint(s) 229 stored in memory 227 may be provided to orotherwise determined by the IoT device 120 in accordance with anysuitable technique. In on example, a user device 211 is coupled to theprocessor 210 and can be used to indicate to the processor 210 that theprocessor 210 is to enter a training mode in which the processor 210determines a fingerprint of a wireless signal it receives and store thefingerprint in memory 227 for subsequent use to enable the main radio122. In another example, a user can program one or more fingerprints 229via a graphical user interface implemented on a computer system externalto the IoT device 120 and cause the external computer system to transmitthe fingerprint to the IoT device for storage in memory 227.

FIG. 3 illustrates an example of a method performed by an IoT device(e.g., IoT device 120) to validate a transmitter by way of RFfingerprinting. At 306, the IoT device communicates with the othertransmitter and, at 308, determines and stores a fingerprint of thetransmitter. Fingerprint techniques such as those described above can beemployed. The main radio 122 of the IoT device may be awake during steps306 and 308 and may be used to provide signals from the transmitter tothe IoT device's processor 210 for determination of the fingerprint. Theprocessor 210 may store the fingerprint in memory 227.

At 310, the main radio 122 is transitioned to a low power state (e.g.,sleep, hibernation). In one example, the processor 210 sends a signal tothe main radio 122 to transition to the low power state following themain radio's use to reply to a request received from a transmitter. Inanother example, the processor 210 sends a signal to the main radio 122to transition to the low power state upon timeout of a timer during aperiod of non-use of the main radio 122.

At 320, the fingerprinting wake-up radio (which remains on andoperational) begins to receive a wireless signal. The wireless signalreceived may be from a valid or invalid transmitter. If the wirelesssignal is from a valid transmitter, the main radio 122 should betransitioned to its higher power (operational) state, but if thewireless signal is not from a valid transmitter, the main radio 122should not be transitioned to its higher power state and thus remain inits low power state. As explained above, a valid transmitter is atransmitter to which the IoT device is paired and with which the IoTdevice should communicate. The wireless signal received at 320 mayinclude reception of a preamble of an IEEE 802.11 message. Transitioningthe main radio 122 to the higher power state may include one or more of:turning power on to the main radio, increasing the operational voltageto the main radio, clocking the main radio at a higher frequency, etc.

At 330, the method includes extracting a feature from the receivedwireless signal. In one example, the extracted feature includes acomputation of the PSD of the received wireless signal as describedabove. The fingerprinting wake-up radio 126 may compute the PSD of thereceived wireless signal.

At 340, the method includes determining whether the extracted featurematches any features stored in memory 229 within the IoT device 120. Inone implementation, the fingerprinting wake-up radio 126 makes thisdetermination. In another example, the fingerprinting wake-up radio 126provides the extracted feature to the processor 210, and the processor210 compares the extracted feature to the feature(s) stored in memory227. In either case, a comparison is made of the newly extracted featureto any features previously stored in memory 227. The extracted featureand the feature(s) stored in memory 227 may comprise PSDs of, forexample, a preamble of wireless packet.

At 350, if the extracted feature does not match any feature(s) stored inmemory 227, then the power state of the main radio 122 remains in thelow power state, that is, the main radio 122 is not awakened.

At 360, if the extracted feature does match at least one feature storedin memory 227, the main radio is awakened and continues to decode thereceived signal. In one example, the fingerprinting wake-up radio 126determines the match and sends a signal to processor 210 to awaken themain radio 122. In another example, the fingerprinting wake-up radioextracts the feature from the wireless signal at 330 and provides thefeature to the processor 210, and the processor 210 determines a matchexists and commands the main radio 122 to be transitioned to its higherpower state (e.g., by providing an enable signal to the main radio 122).Once the main radio 122 is transitioned to its higher power state, themain radio continues receiving the incoming wireless signals andprovides such signals to the processor 210 for further processing. Whilein the higher power state, the main radio 122 also can be used totransmit data (e.g., sensor data).

The term “couple” is used throughout the specification. The term maycover connections, communications, or signal paths that enable afunctional relationship consistent with the description of the presentdisclosure. For example, if device A generates a signal to controldevice B to perform an action, in a first example device A is coupled todevice B, or in a second example device A is coupled to device B throughintervening component C if intervening component C does notsubstantially alter the functional relationship between device A anddevice B such that device B is controlled by device A via the controlsignal generated by device A.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. A first network device comprising: a firstwireless receiver configured to: transition between a low power stateand a high power state; and while in the high power state, receive afirst wireless signal that contains data from a second network device; asecond wireless receiver configured to, while the first wirelessreceiver is in the low power state, receive a second wireless signal;and a processor coupled to the first wireless receiver and the secondwireless receiver and configured to: determine a first fingerprintassociated with the second network device based on the first wirelesssignal; determine a second fingerprint associated with the secondwireless signal; compare the second fingerprint to the first fingerprintto determine whether the second wireless signal is associated with thesecond network device; and based on the second wireless signal beingassociated with the second network device, cause the first wirelessreceiver to transition from the low power state to the high power state.2. The first network device of claim 1, wherein the second fingerprintis based on a power spectral density of the second wireless signal. 3.The first network device of claim 2, wherein the first fingerprint isbased on a power spectral density of the first wireless signal.
 4. Thefirst network device of claim 2, wherein: the first wireless signalincludes an IEEE 802.11a preamble; and the first fingerprint is based ona power spectral density of the IEEE 802.11a preamble of the firstwireless signal.
 5. The first network device of claim 1, wherein: thefirst wireless receiver is configured to couple to a first antenna; andthe second wireless receiver is configured to couple to a second antennathat is different from the first antenna.
 6. The first network device ofclaim 1, wherein the processor is configured compare the secondfingerprint to the first fingerprint associated with the second networkdevice based on the second network device being paired with the firstnetwork device.
 7. The first network device of claim 1 furthercomprising a memory coupled to the processor and configured to store thefirst fingerprint.
 8. The first network device of claim 1 furthercomprising a sensor coupled to the processor and configured to provide aset of sensor data.
 9. The first network device of claim 8 furthercomprising a radio that includes the first wireless receiver, whereinthe radio is configured to transmit the set of sensor data.
 10. A firstnetwork device comprising: a sensor configured to provide a set ofsensor data; a first radio coupled to the sensor and configured to:transition between a low power state and a high power state; and whilein the high power state: receive a first wireless signal from a secondnetwork device; and transmit the set of sensor data to the secondnetwork device; a second radio configured to receive a second wirelesssignal; and a processor coupled to the first radio and the second radioand configured to: determine a first fingerprint associated with thesecond wireless signal; compare the first fingerprint to a secondfingerprint associated with the second network device to determinewhether the second wireless signal is associated with the second networkdevice; and based on the second wireless signal being associated withthe second network device, cause the first radio to transition from thelow power state to the high power state.
 11. The first network device ofclaim 10, wherein: the first fingerprint is based on a power spectraldensity of the second wireless signal; and the second fingerprint isbased on a power spectral density of the first wireless signal.
 12. Thefirst network device of claim 11, wherein: the first wireless signalincludes an IEEE 802.11a preamble; and the second fingerprint is basedon a power spectral density of the IEEE 802.11a preamble of the firstwireless signal.
 13. The first network device of claim 10, wherein theprocessor is configured compare the first fingerprint to the secondfingerprint associated with the second network device based on thesecond network device being paired with the first network device. 14.The first network device of claim 10 further comprising a memory coupledto the processor and configured to store the second fingerprint.
 15. Amethod comprising: receiving, by a first receiver, a first wirelesssignal from a transmitting device; determining a first fingerprintassociated with the first wireless signal; receiving, by a secondreceiver that is different from the first receiver, a second wirelesssignal; determining a second fingerprint associated with the secondwireless signal; comparing the first fingerprint to the secondfingerprint to determine whether the second wireless signal isassociated with the transmitting device; and determining whether totransition the first receiver from a low power state to a high powerstate based on whether the second wireless signal is associated with thetransmitting device.
 16. The method of claim 15, wherein: the firstfingerprint is based on a power spectral density of the first wirelesssignal; and the second fingerprint is based on a power spectral densityof the second wireless signal.
 17. The method of claim 16, wherein: thefirst wireless signal includes an IEEE 802.11a preamble; and the secondfingerprint is based on a power spectral density of the IEEE 802.11apreamble of the first wireless signal.
 18. The method of claim 15,wherein the comparing of the first fingerprint to the second fingerprintis based on a pairing relationship with the transmitting device.
 19. Themethod of claim 15 further comprising: receiving sensor data; andtransmitting the sensor data to the transmitting device.
 20. The methodof claim 19, wherein the transmitting of the sensor data is performed bythe first receiver.